Fire alarm system



May 11, 1954 c, EVANS 2,678,433

FIRE ALARM SYSTEM Filed July 20, 1950 z I4 24 1 x +/7 2 V V ALARM m-zvuc:

25 E-l'l'l' 30 22 fi m -\J+ FIG. I

INVEN TOR.

F. C.. EVANS AT TORNEY Patented May 11, 1954 FIRE ALARM SYSTEM Francis 0. Evans, Richmond, N. Y., assignor to American District Telegraph Company, Jersey City, N. J., a corporation of New Jersey Application July 20, 1950, Serial No. 174,898

2 Claims. he 1 The present application is a continuation-inpart of application Serial No. 789,509, filed December 3, 1947, now abandoned. Application Serial No. 789,509is a continuation-in-part of application Serial No. 423,131, filed December 16, 1941, now Patent 2,432,145, issued December 9,

This invention relates to fire alarm systems and more particularly to such systems employing thermocouple elements for the generation of potential to operate alarm devices.

The term thermocouple used in this specification and in the claims is to be construed as defining a literal thermocouple or a thermopile trated heat is projected into the protected space i at intervals. For example, if a plurality of thermocouples are connected in series through alarm operating mechanism, and if a sudden blast of heat impinges upon such thermocouples, the generated potential may be sufiicient to immediately actuate the alarm mechanism.

An object of the present invention is to provide compensation for a system of the above character whereby the effect of a concentrated blast of heat is ineffective to operate the alarm mechanism.

Another object of the invention is to provide mechanism which can be placed adjacent the heating element in such position that the efiect of the heat blown from the element upon the compensating mechanism will balance the eiiect of the heat on the thermocouple elements.

Another object of the invention is to provide compensation as before described in which control of the effect of the compensating device can be maintained.

In carrying out the foregoing and other objects of the invention a fire alarm system employing the present improvements makes use of a plurality of thermocouples or thermopiles disposed about the premises to be protected, which premises has therein one or more heat dispersers of the type commonly known as blower heaters.

Located in the path of dispensed heat and closely adjacent to the heating element is a unit made up of a thermocouple'or thermopile with associated resistor or resistors which can be regulated to vary the effective potential output of the thermocouple. The compensator thermocouple is connected in circuit with the alarm thermocouples in such fashion that potential generated by the compensator bucks the potential generated by the alarm thermocouples so that if such potentials are equal, no alarm will result. Such an arrangement has no deleterious effects on the efiiciency of the system for fire alarm purposes since the alarm thermocouples are of such number that if an alarm condition arises the combined potentials of the alarm thermocouples will more than balance the bucking potential of the compensator thermocouple with the result that a potential of such value is fed to the alarm mechanism as to cause the operation of this mechanism for alarm purposes. In one type of compensator the adjustable resistor elements are connected in parallel to the thermocouple element for close adjustment while in another form of compensator element an adjustable resistor is connected in series with the thermocouple element for such adjustment. In either form of the invention the resistor or resistors can be eliminated from the circuit so that the full effect of the compensator thermocouple potential will be introduced into the circuit of the alarm thermocouples.

Other features, objects and advantages of the invention will become apparent by reference to the following detailed description of the accompanying drawings, wherein:

Fig. 1 is a front view of a conventional blower heater;

Fig. 2 is a plan view of a system associated with such a blower heater;

Fig. 3 is a circuit diagram of one type of compensator; and

Fig. 4 is a similar view of a modified form of compensator.

Referring now to the drawings and to Fig. 1, I!)

indicates generally a blower heater of the type common to industrial premises, meeting places, and the like, such heater usually being gas-fired and having a motor driven fan for directing strong heated currents of air.

When such a heater or heaters are installed in premises, it is evident that intermittent blasts of warm air are distributed throughout the premises with the result that if use is made of thermocouple fire alarm devices, distributed usually about the roof of the premises, these thermocouple elements will be intermittently heated to such an extent as to generate a considerable potential. The potential thus generated normally would be sufficient to actuate an alarm mechanism associated therewith with the result that an alarm would be given at each operation of the blower heater. Referring to Fig. 2 it will be seen that a plurality of alarm thermocouples indicated at I2, l4, I6, and. it are connected in series through a relay l9 and a meter whereby if the potential generated by these thermocouples in a closed circuitis sufficient to energize the relay l9, such relay will pick up its armature 2| and close contacts 22 serving to energize an alarm device 24 having a source of potential 25 in circuit therewith.

However, in order to neutralize the effect of the intermittent blasts of hot .air-supplied'by the blower, a compensating device indicated generally at is included in the circuit of thealdr'm thermocouples with the polarity of the cornpensator in opposed relation to the'pol'ar'ity of the alarm thermocouples. preferably located immediately in front of the .blower heater so that thehot air discharged by 7 this. heater can have a more pronounced effect on the compensator than on the alarm thermocouples". Thus, ifjthe compensator is correctly ,zadjuis'teda potential will be generated thereby Tin opp'ositionto the potential generated, by the ."combined alarm thermocouples and of the same .value so that the relay i9 is not energized.

Each alarm thermocouple element is of conventional character preferably, but not necessarily, a thermopile, being made of a number .of hot and cold junctions'of dissimilar metal so arranged that when the hot, junctions are at a temperature higher than the cold junctions, a pote'ntialwill begen'erated.

:The compensator element enclosed in the unit 30 com-prises (Fig. 3) a thermocouple of like nature indicated at made up of a number of joints of dissimilar metal and connected to terminals'fifi sand 31. These terminals 36 and 3? r can be, connected in the line 38 which serves to connect thealarm thermocouples in series. How- -ever,. it will be noted that the polarity of the thermocouple 35 is reversed relativeto the polarity fof the alarm thermocouples so that the potential. generated by the thermocouple 35 will buck the potential generated by the alarm thermocouples. Associated with the terminals 35 and. are a plurality of resistors 40, which can be. ;connected selectively in parallel with these terminals by means of the switch H- which has ::a sweep to engage the contact points between the resistors in effect are shunted out of the circult with the result that the full potential generated by the thermocouple .35 Will be introduced into the circuit of the alarm thermocouples.

-Likewise, if the sweep ill is moved into contact with a point it, the result will be that the thermocouple s5 is in effect short-circuited so far as its influence on the alarm circuit is concerned. .In Fig, 4 a 'modification of the compensator .;has:been shown, such modification comprising a thermocouple connected to terminals SI and 52. Associated with this thermocouple 50 is a variable resistor 54 which can be operated either to introduce resistance in series with the thermocouple and the. line 38 or to be shorted out of the circuit so that the full eiiect of the thermocouple 35 .can be'utilized. For example, if the compensator isconnected in the line 38 as shown This compensator is.

1 mediate position along resistor 54, the effect will 4 in Fig. 4, and if the sweep 55 is in an intercouples In utilizing either compensator element as shown .in Figs. 3 and 4, it will be evident that these devices can be adjusted by operation of the sweeps 41 or 55 while the blower heater is in operation until the effect of the com'pensating potential nullifies the effect of the potential generated by the alarm thermocouples, which condition will be evidenced by the meter 20. 'Furthermore, it will :beevident that if a single compensator is not suflicient to produce thedesired results, additional com-pensators can be introduced into the circuit by installing the same in the alarm circuit and positionedadjacentthe blower heater, or in any other advantageouslocation about the premises.

With the compensatoredjusted to nullify the potential generated by the alarm, thermocouples while the blower heater is in operation, analarm can still "be given if a condition ,of fire occurs since the heat supplied by suchfire .willseryeto increase the potential generated by one or -more of the alarm thermocouplesthereby upsetting the balanced condition in the alarm circuit and causing the relay It to close the contacts 22.

From theforegoing it will be seenv that the present invention provides improved compensation for fire alarm systems installed in premises employing. heaters of the intermittent blast type. It will be evident that modifications beyond the illustrated embodiments can bemade, andaccordingly any limitations imposed on the invention are to be only those set forth'in the followins claims.

What is claimed is:

,1. In a system .for detecting fire in a supervised region of premises which are subjected intermittently to non-hazardous heat froma nonhazardous, intermittent heat source, in combination a plurality of alarm thermocouplesnspaced apart about said supervised region forgenerating a voltage in response to rises in the temperaature in said supervised region of said premises,

a compensator thermocouple located closer to said non-hazardous source than is any one .LOf said alarm thermocouples, said compensator thermocouple being positioned to receive more heat'from said non-hazardous source during its operating intervals than does any of said :alarmthermocouples, alarm means, alarm actuating means connected in a seriescircuit with said alarm thermocouples and said compensator thermocouples,

said alarm thermocouples beingin a voltage. additive relationshipto one another, ;but:in;a voltage opposing relationship to said alarm thermocouple,

said alarmthermocouple beingadapted to. generate a great enough voltage in response toheat from said non-hazardous source that if not attenuated, said voltage wouldover-compensate for the voltage generated by said alarm thermocouples in response to heat .jfrom, said .non-

hazardous source, and a variable resistor connected across the terminals of said compensator thermocouple in shunt therewith, said resistor being adjusted to a value of resistance which will attenuate the effective voltage from said compensator thermocouple to a value which will substantially balance the voltage from said alarm thermocouples during intervals when heat is received solely from said non-hazardous source and thereby suppress actuation of said alarm, but said value of resistance being small enough to limit the possible effective voltage from said compensator thermocouple to a value small enough to enable said alarm thermocouples to actuate said alarm when fire occurs in said supervised region, even when heat is being received by said compensator thermocouple from said non-hazardous heat source.

2. In a system for detecting fire in a supervised region of premises which are subjected intermittently to heat from a non-hazardous heat source, in combination, a plurality of alarm thermocouples connected additively in series and spaced apart about said supervised region of said premises, for generating a voltage in response to rises in the temperature in said supervised region, a compensator thermocouple spaced apart from said alarm thermocouples, said compensator thermocouple and said alarm thermocouples being positioned so that said compensator thermocouple is closer to said non-hazardous heat source than is any one of said alarm thermocouples and receives more heat originating in said non-hazardous source than does any of said alarm thermocouples, alarm actuating means connected in a series circuit with said alarm thermocouples and said compensator thermocouple, said compensator thermocouple being connected in said series circuit with a polarity opposed to that of said alarm thermocouples, a plurality of resistors connected in series combination, a plurality of stationary contacts individually connected to junctions between said resistors, a movable contact member adapted selectively to engage any one of said stationary contacts, means connecting one terminal of said compensator thermocouple to one end of said series combination of resistors, means connecting its other terminal to said movable contact member, said movable contact member being so positioned as to engage one of said stationary contacts which will provide an effective resistance across the terminals of said compensator thermocouple great enough so that during intervals when heat is being received solely from said non-hazardous source the voltage from said compensator thermocouple is great enough to suppress actuation of said alarm by said alarm thermocouples, but said resistance being small enough to limit the possible efiective voltage from said compensator thermocouple to a value small enough to enable said alarm thermocouples to actuate said alarm when fire occurs in said supervised region, even when heat is being received by said compensator thermocouple from said non-hazardous heat source.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,432,145 Evans Dec. 9, 1947 2.4 ,675 Rutherford Nov, 8, 1949 

